The invention relates generally to microwave heating, curing, and drying devices and, more particularly, to microwave applicators in which two collinear arms of a waveguide T-junction form an exposure tunnel through which materials are conveyed and subjected to uniform microwave exposure.
In many continuous-flow microwave ovens, a planar product or a bed of material passes through a waveguide applicator in or opposite to the direction of wave propagation. These ovens are typically operated in the TE10 mode to provide a peak in the heating profile across the width of the waveguide applicator midway between its top and bottom walls at product level. This makes it simpler to achieve relatively uniform heating of the product. But TE10-mode applicators are limited in width. Accommodating wide product loads requires a side-by-side arrangement of individual slotted TE10 applicators or a single wide applicator. The side-by-side arrangement is harder to build and service than a single wide applicator, but wide applicators support high order modes, which can be difficult to control. The result is non-uniform heating across the width of the product. Another problem is that the dielectric properties of materials to be heated vary with thickness and moisture content, for example, and from one material to another. Many microwave oven configurations are highly sensitive to the dielectric properties of material loads and are tailored to heat specific materials. These ovens may not heat other materials well. Furthermore, tuning microwave oven cavities to reduce reflections and to maximize power transfer to the load is often difficult with stub tuners that extend into the cavities.
Thus, there is a need for a continuous-flow microwave oven capable of uniformly heating a range of material loads across the width of the oven and that is easy to tune for a range of materials.